1. Field of the Invention
The present invention relates to a plunger pump for injecting fuel by reciprocating a plunger, and particularly to a single-cylinder type plunger pump for supplying fuel to a common rail of an engine.
2. Description of the Related Art
Generally, in a fuel injection apparatus for directly injecting fuel into a combustion chamber of an internal combustion engine, a configuration having a damper for reducing pressure pulse of fuel is known.
In this kind of fuel injection apparatus, low-pressure fuel supplied from a low-pressure pump is pressurized to supply high-pressure fuel to a common rail. For this reason, there is known a configuration comprising a damper for reducing pressure pulsation in the apparatus in order to decrease pressure pulsation of fuel to be supplied under pressure.
For example, Japanese Patent Unexamined Publication Hei No. 7-83137 discloses a configuration in which an accumulator (damper) is provided at a discharge side (fuel outlet side) of a high-pressure pump. In this accumulator, the pressure of the fuel, which a diaphragm receives, is reduced by a spring provided at a back pressure side of the diaphragm.
Also, Japanese Patent Unexamined Publication Hei No. 9-177634 discloses the configuration in which a spring-type accumulator reservoir (damper) is provided at a suction side (fuel inlet side) of a high-pressure pump.
In a single cylinder type plunger pump, which pressurizes fuel by reciprocation of the plunger, however, pressure pulsation occurs on both the fuel suction side and the fuel discharge side. For this reason, if the damper is provided at either the fuel suction side or the fuel discharge side, there is a problem in that noise and vibration caused by pressure pulsation cannot be sufficiently reduced.
In order to solve such a problem, it can be considered that the damper for reducing pressure pulsation is provided at each of the fuel suction side and the discharge side.
In this case, it is considered that the spring-type damper as disclosed in the above publication is provided at each of the fuel suction side and the discharge side. However, in the configuration using the spring on the back pressure side of the damper, rubber is used as a diaphragm and such a rubber diaphragm is susceptible ot deterioration caused by the fuel. For this reason, there is a problem in that reliability is low.
Moreover, the use of the spring to apply back pressure requires a space for containing the spring. This causes a problem in that the apparatus becomes large-sized.